1. Field of the Invention
The present invention relates to a connection of steel pipes for conveying solid materials, particularly for conveying gravel.
2. Description of the Related Art
Solid materials, for example, gravel or sand, or also washery refuse and construction materials, are conveyed or transported in strands of pipes which are composed of several steel pipes that are releasably connected to each other. Depending on the type of use, the pipe strands remain placed in one place for a longer period time. However, in other cases, it may be necessary to place the strand at a different location or to extend or shorten the strands within certain time intervals, possibly short intervals.
Because of the high mechanical stresses to which the steel pipes are subjected by the conveyance of solid materials, the pipes are subjected to a high wear essentially over the entire axial length. Consequently, it must be possible to manufacture the steel pipes inexpensively. Moreover, since not all steel pipes which form the strands of pipes wear on the inside thereof as a result of the conveyed solids and since the steel pipes may additionally be subjected to different stresses from the outside, it is also necessary to be able to easily and quickly remove individual steel pipes from an otherwise closed permanent strand of pipes and to be able to insert new steel pipes into the strand without problems.
Consequently, for replacing the pipes and to make it possible to easily place the pipes at a different location, two successive steel pipes in a strand of pipes abut each other in an uncentered manner. Centering means which engage into each other are not provided because this would mean that substantial operations would be required for radially removing a steel pipe from a strand of pipes as well as for inserting a new steel pipe into the strand. This is because several successive steel pipes would have to be separated from each other at the joints and would have to be displaced in axial direction in order to provide sufficient room at the locations of the two joints at the end faces of the steel pipe to be replaced, so that this steel pipe can be removed radially from the strand of pipes and a new steel pipe can be inserted. Subsequently, all axially displaced steel pipes would have to be returned into the original position and would have to be coupled to each other again in a tight manner. In addition, it must be taken into consideration that for each joint it is necessary to remove several coupling bolts which are located on a pitch circle and to return the coupling bolts into the properly oriented positions.
Because two successive steel pipes are joined together uncentered and due to the great tolerances which inevitably occur because of manufacturing reasons of the positions of the receiving bores in the coupling flanges relative to the longitudinal axes of the steel pipes, impact edges may be formed in the interior of the steel pipes in the area of the joint between two steel pipes. Even if the impact edges are small, this has the result that the solid particles being conveyed in the steel pipes are deflected and swirled at the impact edges and hurled against the inner wall surfaces of the steel pipes. This leads to substantial wear phenomena at these locations. These phenomena can be observed especially at the inlet sides of the steel pipes.
In this connection, it must be taken into consideration that the impact area between two steel pipes is not only subjected to wear, but also to a bouncing load resulting from the impinging solid particles.
The steel pipes may be single-layer pipes, or multiple-layer pipes.